<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div id="root"></div>
    <script src="./lib/react.js"></script>
    <script src="./lib/react_dom.js"></script>
    <script src="./lib/babel.js"></script>

    <script type="text/babel">
      class App extends React.Component {
        constructor() {
          super();
          this.state = {
            counter: 0,
          };

          this.increment = this.increment.bind(this);
          this.decrement = this.decrement.bind(this);
        }

        increment() {
          this.setState({
            counter: this.state.counter + 1,
          });
        }

        decrement() {
          this.setState({
            counter: this.state.counter - 1,
          });
        }

        render() {
          const { counter } = this.state;
          return (
            <div>
              <h2>{counter}</h2>
              <button onClick={this.increment}>+1</button>
              <button onClick={this.decrement}>-1</button>
            </div>
          );
        }
      }

      const root = ReactDOM.createRoot(document.querySelector("#root"));
      root.render(<App />);
    </script>
  </body>
</html>
